Happening as it does deep within the Earth’s mantle, the process of creating diamonds has always been a bit murky. Laypeople understand the explanation has something to do with enormous pressure exerted on carbon. Hollywood once portrayed the process, perhaps just a tad simplistically, when it showed Superman producing a diamond by squeezing a lump of coal in his hand. But a paper published by the academic journal Nature on August 19 suggests ancient seawater played a key role, at least in the diamonds of the Northwest Territories’ Slave Craton.

While polished diamonds are coveted for their beauty, some rejects offer clues about the gems’ genesis.

A team of scientists examined 11 stones from the Fox kimberlite at Dominion Diamond’s (TSX:DDC) majority-held Ekati mine and compared them with others from Ekati’s now-depleted Panda kimberlite and the Dominion/Rio Tinto NYE:RIO Diavik mine. The diamonds were rejects, partly because of their puny size and prominent inclusions, or impurities. But those inclusions revealed something of value to researchers—“a variety of fluid compositions plus inclusions of their host rocks … which shows a strong association between fluid composition and mantle host lithology.”

CBC’s Emily Chung translated the boffin-speak: “What they found was very high concentrations of sodium and chlorine—the main components of the salt dissolved in seawater. And when they looked at the pattern of the kinds of strontium in the sample, it was ‘very similar to dissolved strontium in ancient seawater several hundred million years ago,’ [geochemist Graham] Pearson said.

“The researchers couldn’t come up with any other explanation for all the salt, he added. ‘There’s nowhere really in the deepest parts of the earth that are obvious sources of all that sodium and chlorine.’

“That led the researchers to conclude that the source of the fluid was ancient seawater pushed under the Northwest Territories with nearby tectonic plates … The seawater would have interacted with carbon-containing rocks to generate diamonds.”

More importantly, the findings offer “another key element in the picture of how water is cycled and carbon is cycled in the Earth,” Chung quoted Pearson. “This is really more evidence of recycling of fluid of water within the Earth.”